When ENUM domains become active, users will be identified by their telephone number including the country code. What that means is a phone number such as +46-8-9761234 would be mapped to the 4.3.2.1.6.7.9.8.6.4.e164.arpa Internet address in a process that is expected to become automated and transparent to the user.

So, basically, if you have any single aspect of someone's contact information--even if it's just a phone number or fax number--you automatically can figure out all the various ways to contact that person: mobile phone, email, instant messaging, etc.

The comments at the referring page bring up a lot of the obvious concerns. Anonymity on the Net becomes much harder under something like this, unless you're really determined to mask yourself (and in some cases, for good or bad intent, you are). The worst aspect of it is, of course, the big boon it is for telemarketers and other slime, who will use this as a means to annoy ever more people every more completely.

The problem with this is that it's, at first glance, pretty innocuous, which is why chances are very good it will come into being without a hitch.